FIG. 8 is a partial cross-sectional view showing a configuration of a sealing portion of a conventional electric double layer capacitor. The capacitor has a substantially cylindrical capacitor element (not shown), cylindrical case 11, which is made of metal, has a bottom, and accommodates the capacitor element, terminal plate 12, and sealing rubber 13.
One electrode of the capacitor element is connected to terminal plate 12. The other electrode thereof is connected to a bottom surface of case 11. That is, case 11 functions as one of terminals.
Flange portion 12D is provided horizontally along a peripheral edge at a lower end of an outer peripheral surface of terminal plate 12. Ring-shaped sealing rubber 13 made of an insulating rubber is fitted onto the outer peripheral surface of terminal plate 12 so as to be abutted and positioned onto flange portion 12D. Then, sealing rubber 13 is compressed between drawn and grooved portion 11A provided to a side surface of case 11 and the outer peripheral surface of terminal plate 12 from an outside of the side surface of case 11. Thereby, an opening of case 11 is sealed to secure airtightness, and case 11 is insulated from terminal plate 12.
Further, sealing rubber 13 is pressingly contacted and held onto case 11 by curled portion 11C of arc cross section, formed by processing an end of the opening of case 11 so as to curl it toward an inside diameter of case 11 (typically, called curling processing).
In this way, the capacitor can increase an area of an outer peripheral surface of sealing rubber 13 which is compressed by groove-processing with respect to the outer peripheral surface of case 11, and the amount of compression thereof. Therefore, improvement of airtightness can be enhanced to improve reliability. In addition, a shape of sealing rubber 13 can be simplified to make manufacturing easy (for instance, PTL 1).
In the above configuration, sealing rubber 13 is compressed between the outer peripheral surface of terminal plate 12 and drawn and grooved portion 11A provided onto the side surface of case 11 to hold a sealed state. However, when there is a slight flaw or dent on the outer peripheral surface of terminal plate 12, an electrolyte can leak from the flaw. Such flaw and dent can be caused when a stamping mold for manufacturing terminal plate 12 is damaged or a large number of terminal plates 12 are conveyed together. Therefore, the above sealing configuration is required to further enhance reliability against the leakage of electrolyte.
Citation List
Patent Literature                PTL 1: Unexamined Japanese Patent Publication No. 2007-189184        